Two-step rocket propellant injection system



March 11, 1969 J. T. HAMRICK 3,431,733

TWO-STEP ROCKET PROPEL LANT INJECTION SYSTEM Filed July 5, 1965 l5 /9 I30 I I0 2/ I j .V v 23 /5 la INVE'VTOR.

JOSEPH r HAMR/CK United States Patent 3,431,733 TWO-STEP ROCKETPROPELLANT INJECTION SYSTEM Joseph T. Hamrick, 6364 Jae Valley Road SE.,Roanoke, Va. 24014 Filed July 5, 1966, Ser. No. 562,904 US. Cl. 60--258Int. Cl. F02k 9/02; F02g 3/00 1 Claim ABSTRACT OF THE DISCLOSURE Thepresent invention relates broadlly to decomposition of monopropellantfuels suitable for rocket propulsion and gas generation, and is moreparticularly concerned with injection of propellant into a chamberemploying a decomposition catalyst without damaging the catalyst bed atstart up.

It is the primary aim of the present invention to provide an injectionsystem which automatically limits the amount of propellant introducedinto the catalyst bed at start up, thereby preventing flooding of thecatalyst bed with propellant before the catalyst bed reaches an operabletemperature.

Another objective of the invention is to provide an improved method ofholding the catalyst particles in place for more effective and uniformdecomposition of the propellant and better resistance to shock andvibration.

A further objective of the invention is provision of an insulatinglining material of low heat capacity to reduce the amount of heatconduction from the rocket chamber body to the propellant injector,especially after shut down of the rocket motor.

Other objects and advantages of the present invention will become moreapparent during the course of the following description, particularlywhen taken n connection with the accompaying drawing.

In the drawing wherein like numerals are employed to designate likeparts throughout the same:

FIGURE 1 is a fragmentary :perspective view of one form of rocket or gasgenerator chamber which may be employed in the practice of the method ofthe invention.

FIGURE 2 is a detail of the propellant injector of this invention.

Applicants invention lies in the discovery that a mechanical arrangementcan be devised for limiting the amount of fuel introduced into thecatalyst bed until adequate pressure is generated to actuate theinjector in such a manner as to allow full flow of the propellant.Numerous starts with commercially available catalysts, especially thoseusing carriers composed of pressed alumina pellets with large internalsurfaces, have shown that injection of the full rated flow of propellantinto the catalyst bed frequently results in flooding of the bed withconsequent failure to start immediate decomposition. A secondary effectof this failure is that after shut down of the fuel subsequent tofailure to start, the catalyst gradually generates adequate heat toexplosively decompose the residual propellant in the chamber and crushthe alumina carrier. Crushing of the bed results in blockage of the flowof gaseous decomposition products and renders the catalyst bed unusableand dangerous.

The utilization of a two-step injection system allows a slow rate ofpropellant injection until the catalyst bed temperature is increased tothe point where it is adequately reactive to admit full propellant flow.When propellant is injected onto the catalyst bed and the temperature ofthebed rises due to propellant decomposition, there is also a rise inchamber pressure. The present invention of a two-step injection systemis based on utilization of the accompanying pressure rise.

Referring now to FIGURES l and 2, there is shown a rocket chamberdesignated by the numeral 10 and employing a two-step propellantinjector with catalyst bed and fused silica liner.

A pressurized monopropellant is fed through an appropriately attachedline to inlet 1E1, passes through planetary holes 12 across spring 13into annulus 14 around pintle 15 and through small holes 16 and into thedecomposition chamber. Propellant seals 17 and 18 prevent propellant orgenerated gases from passing around injector seat 19. Any small leakagewhich occurs is vented through the port 20 in the injector head causing21. Fuel is sprayed through the small holes onto catalyst bed 22 whichconsists of segmented compartments composed of separator 23, supports 24and 25 and retention pin 26. Separator 23 is perforated so that thepropellant and decomposed gases may pass through and around the pelletsin the catalyst bed. Upon contacting pellets the propellant decomposesthereby heating up the catalyst bed and building up pressure in thechamber. As the pressure builds up it exerts a force against theinjector seat 19 greater than the force exerted by the fuel on theopposite end which has only a small area in contact with the propellant.Upon the injector seat being moved away from the pintle, the full flowrate of the propellant is allowed and the rocket is Operating at ratedconditions. The fused silica liner which must be made in multiplesections before being place in the rocket chamber shell 28 serves as alow heat capacity insulator to prevent the shell 28 from heating uprapidly. The thickness of the liner 27 will, of course, determine thelength of time before the chamber shell 28 heats up. By thus preventingthe rapid heating up of the shell 28, the amount of heat available forconduction to the injector head 21 is reduced and the danger ofexplosively decomposing the residual fuel left in the head after shutdown can be reduced or eliminated. By utilizing the segmentedcompartments for retention of the catalyst particles, maximum controlover placement of the particles is maintained. This is important to thefunctioning of the chamber for the following reasons:

(*1) The distance from the point of propellant admission to the catalystbed should remain constant for uniform performance. The compartmentedarrangement helps to do this.

(2) )With a large compartment, catalyst pellets move a larger distanceand acquire greater momentum during high amplitude vibrations thusincurring greater damage to the pellets.

(3) For chambers with the centerline in a horizontal position relativeto the earths gravitational field, it is possible to bypass the catalystbed in the void between the catalyst bed and the shell with a looselyfilled compartment. With the arrangement shown the statistical chancesof bypassing the catalyst bed in the above manner are lessened. Y

(4) Chances of packing the catalyst bed due to explosion are greatlylessened due to the fact that pressure exerted on one end of thecatalyst bed would not necessarily be transmitted to the entire bed dueto the supports 24 and 25.

Gases generated by decomposition of the propellant are exhausted throughthe nozzle throat 29. Gases are prevented from escaping at the junctionof the injector head 21 and chamber shell 28 by means of copper gasket30. The injector head 21 is held to the chamber shell 28 by means ofthreads which offer a convenient means of assembly and disassembly ofthe rocket chamber. The catalyst bed assembly is held in place bysegments of the fused silica liner 27. The conical section of silicaliner downstream of the throat 29 is held in place by crimping the shell28 around the cone exit. Upon shut down of the rocket motor, lpintleseat 19 resumes its closed position due to the pressure exerted byspring 13.

Example rocket chamber The compartments of the catalyst bed 22 arefilled with .10 pounds of commercially procured catalyst pellets As-inchdiameter by %-inch long. The catalyst pellets are equally distributedamong the 1 1 compartments of the catalyst bed. Anhydrous hydrazine, themonopropellant fuel, is spray-injected through the injector head at arate of .2 to 2 pounds per minute. As the pressure increases in thechamber the pintle seat 19 is forced away from the pintle -15 and thefull rated flow of approximately 2 pounds per minute is allowed. Thechamber pressure is approximately 180 pounds per square inch gauge andthe throat diameter is approximately .168 inch. The approximate thrustof the rocket at this fiow rate is 5 pounds.

The foregoing quantities have not been tested in the generator shown inFIGURE 1 but were computed on the basis of previous work, some of whichis cited in the reference.

I claim as my invention:

\1. A monopropellant rocket motor comprising a reaction chambercontaining a catalyst bed, means for injecting monopropellant into saidcatalyst bed, and a thrust nozzle, said injection means comprising afixed pintle extending toward said bed and having a flared end, said endhaving at least one aperture for injecting monopropellant, for startingsaid motor, an annular valve piston biased toward said flared end andforming therewith a second aperture for injecting monopropellant fornormal operation of said motor, said valve piston being responsive toreaction chamber pressure to open said second aperture.

References Cited UNITED STATES PATENTS 3/1960 Plescia -3946 9/1964Hickerson 60-258 U.S. Cl. X.R. 60-3914

